27. A rm has a production function f(x, y) = 1.80(x0.80 + y0.80)3 whenever x > 0 and y > 0. When the amounts of both inputs are positive, this firm has a. increasing returns to scale if x + y > 1 and decreasing returns to scale otherwise. b. decreasing returns to scale. c. constant returns to scale. d. increasing returns to scale. e. increasing returns to scale if output is less than 1 and decreasing returns to scale if output is greater than 1